The present invention relates to a thrust reverser for a gas turbine engine and in particular to a thrust reverser provided on a ducted fan gas turbine engine.
Thrust reversers are used on gas turbine engines to reverse the direction of the gas stream and thus use engine power as a deceleration force. On ducted fan gas turbine engines, reverse thrust action is achieved by reversing the fan airflow. As the majority of thrust is derived from the fan sufficient reverse thrust is achieved by reversing the cold fan stream airflow alone.
Thrust reversers on ducted fan gas turbine engines comprise a plurality of doors which can be translated into a position in which they block the fan air outlet. The fan air is then deflected by the doors through a plurality of deflector vanes located in the engine cowling which are exposed by translation of the cowling. The fan air is directed in a generally outward and partially forward direction by the deflector vanes to provide braking.
The deflector vanes are arranged in segments known as cascades which are positioned around the circumference of the engine cowling. To achieve sufficient braking the engine cowling must translate the length of the cascades to expose all the deflector vanes.
In ducted fan gas turbine engines the size of the cascades are determined by the amount of fan air that bypasses the core engine. For high bypass ducted fan gas turbine engines the size of the cascades can lengthen the engine cowling considerably.
GB2182724B, which is owned by the applicant, provides cascades which enable the length of the engine cowling to be shortened. In GB2182724B the vanes are stowed in a stacked relationship which reduces the overall length of the cowling. in order for the deflector vanes to be stacked when stowed they are not securely mounted and the vanes may fail or be damaged during operation of the thrust reverser.
The present invention seeks to provide a thrust reverser which is compact when stowed to reduce the overall length of the cowling but which is less complex and in which the vanes are securely mounted to overcome the aforementioned problems.
According to the present invention a thrust reverser for a gas turbine engine includes a cowl and at least first and second cascade structures, each cascade structure comprising a plurality of air deflecting vanes in fixed spaced relationship, the first cascade being fixed adjacent a fixed portion of the cowl and the second cascade being mounted to translate between a first inoperative position where the second cascade is stowed radially inward of the first cascade and a second operative position where it is moved clear of the first cascade and the cowl to expose the air deflecting vanes.
An annular portion of the cowl is translatable and the translating cascade is preferably mounted on the translating portion of the cowl so that movement of the cowl moves the cascade. The translating portion of the cowl may be intermediate the upstream and downstream ends of the cowl.
In the preferred embodiment of the present invention the cascade structure is stowed within the fixed portion of the cowl in the inoperative position.
The thrust reverser may include blocker doors mounted for operation in a gas duct, the outer wall of which is defined by said cowl, said blocker doors being moveable between a position wherein they block the duct and divert gases in the gas duct to the cascade and a position wherein they provide part of the flow structure of said duct outer wall.